1. Field of the Invention
The present invention relates to a treated inorganic filler material having improved compatibility characteristics when added to certain polymeric substrates and to the filled polymer compositions improved by the presence of the treated filler material.
2. Description of the Prior Art
Inorganic fillers have been used in certain polymers, for example, thermoplastic polymers, to impart dimensional rigidity and lower costs to the resulting blend of filler and polymer. When the filler is added to such polymers at even low loadings, however, certain of the physical properties of such polymers (e.g., impact strength) begin to become adversely affected. Also, a large amount of extra energy is needed to uniformly disperse the inorganic filler in the polymer. In order to overcome these shortcomings, it has been proposed that either: (1) a polar copolymer be added during the polymerization of the polymeric material; (2) coupling agents or other additives be added to either the filler, polymer, or filled polymer composition; or (3) the filled formulation be crosslinked (See Handbook of Fillers and Reinforcements of Plastics, edited by H. S. Katz et al., pp. 112-115, 1978).
The prior art has taught the addition of various types of coupling agents or other additives to the filler material, polymer, or the composite to improve the compatibility of the filler and polymer for one another. For example, U.S. Pat. No. 3,926,873 to I. Aishima et al. advocates the use of aliphatic or aromatic carboxylic acids having from 3 to 11 carbon atoms, one or two ethylenic unsaturations, and one or two carboxyl groups as such a class of additive. A family of titanates, available from Kenrich Petrochemicals, Inc., have also been proposed for use as additives to improve the compatibility of polymer and filler (Handbook of Fillers and Reinforcements for Plastics, supra.; Modern Plastics, December 1974, p. 68; Modern Plastics Encyclopedia, Vol. 53, No. 10A, October 1976, pp. 161 and 166; and U.S. Pat. Nos. 4,094,853 and 4,098,758).
Although the prior art contains a teaching that certain phosphorus-containing compounds can function as coupling agents or adhesion promoters in adhesive systems (see P. E. Cassidy et al., J. Macromol. Sci., Revs. Polymer Technol. Dl (1) pp. 2 and 22-23, 1971), it has not been appreciated that compositions containing hydrocarbyl phosphate and/or pyrophosphate compounds and/or their alkali metal or alkaline earth salts can be used to improve the compatibility of an inorganic filler and polymeric substrate. For example, U.S. Pat. No. 3,404,023 to M. E. Schrader et al. teaches the use of diethyl phosphite (rather than a phosphate or pyrophosphate) to improve the compatibility of glass fibers with a resin substrate. Also, U.S. Pat. No. 3,344,107 to R. E. Miller teaches the use of various phosphorus-containing compounds containing reactive alkenyl, acrylic or methacrylic groups (rather than non-reactive saturated hydrocarbyl groups) as coupling agents between a polymer substrate and a mineral reinforcing agent.